A chain has been used in various known systems including a parking system since it enables an accurate power transmission without any slippage. In a conventional parking system provided with a driving unit having a motor, the power from the motor is normally transmitted to a lift via a chain, for example.
In the parking system, the chain should be frequently monitored for any abnormality because breakage or cutting of the chain may cause serious accidents. However, manually checking the status of the chain, which is usually positioned in a place not easily seen or accessible, is burdensome. For this reason, chain-monitoring devices that can constantly and automatically monitor the status of the chain have been proposed.
FIG. 1 illustrates a prior art device for monitoring abnormality in a chain used in a parking system. The chain-monitoring device 10 is provided with a plate 6, a pair of guiding posts 2, a member 12 and a sensor 4.
As can be seen in FIG. 1, the plate 6 is attached to a stationary component of the parking system. One end of each guiding post 2 is attached to the plate 6, while the other end thereof remains unattached and thus constitutes a free end. The member 12 retained around the guiding posts 2 is vertically movable along the guiding posts 2. Stoppers 14 are formed at the free ends of the guiding posts 2 in order to limit a downward movement of the member 12. A pair of springs 8 vertically biases the member 12 downward for contact with a chain 16. The sensor 4 located on the plate 6 serves to measure the distance between the plate 6 and member 12 by sensing the surface 12a of the member 12.
In the prior art chain-monitoring device 10 described above, the member 12 moves downward when the chain 16 is cut, broken down, or slackened. The change in distance due to the downward movement of the member 12 is detected by the sensor 4. The sensor 4 then informs a controller (not shown), for example, of the abnormality in the chain 16.
In the prior art chain-monitoring device 10, however, since the member 12 is kept in a sliding contact with an uneven surface of the chain 16, the member 12 tends to seriously vibrate. This causes unwanted noise and the portion of the member 12 contacting the chain 16 becomes easily worn out. Further, as the distance between the plate 6 and the member 12 increases due to the wear of the member 12, the sensor 4 may issue a wrong signal that the chain 16 is malfunctioning.